Epoxy thermoset resins can be utilized in a variety of applications including adhesive and structural material applications, e.g., carbon fiber composites for aerospace. The use of aromatic diamine curatives for polyepoxy resins enables the formation of high glass transition temperature (high T.sub.g) crosslinked polymers (thermoset resins). High cure temperatures (often followed by long post-cure heating) are generally required to achieve high performance characteristics.
Many catalysts or accelerators are used to reduce the curing time for aromatic diamine-polyepoxy resins. Typical of these are phenols, imidazoles, boronfluoride-amine complexes, metal fluoroborates such as zinc fluoroborate and copper fluoroborate, and triphenyl phosphite. But latent catalysts for high performance epoxy thermosets remain an industry need.
Japanese Patent Publication No. 57-192428 (Ajinomoto Co., Inc.) discloses a composition comprising an alicyclic epoxy resin, epoxidized butadiene polymer and/or epoxidized soybean oil, trialkanolamine borate, and pyrocatechol or pyrogallol.
U.S. Pat. No. 4,101,459 (Andrews) describes a composition comprising an epoxide resin, an aromatic, heterocyclic, or cycloaliphatic polyamine, and a salt of trifluoromethanesulfonic acid which is used to accelerate the cure.
U.S. Pat. No. 4,331,582 (Babayan) describes a latent catalyst for the reaction of diaminodiphenylsulfone (DDS) with epoxides. The catalyst is the half salt of an imidazole and a strong aromatic sulfonic acid such as toluene sulfonic acid.
U.S. Pat. No. 4,447,586 (Shimp) describes compositions made from polyepoxide resins and hindered aromatic diamines. The cure of these compositions is accelerated with copper fluoroborate.
U.S. Pat. No. 4,593,056 (Qureshi et al.) describes compositions comprising an epoxy resin having at least two 1,2-epoxy groups per molecule, an aromatic diamine hardener, and as a cure accelerator an aromatic trihydroxy compound.
U.S. Pat. No. 4,925,901 (Bertram et al.) discloses compositions comprising: (1) an epoxide containing compound, (2) a phenolic hydroxyl containing compound, and (3) a catalyst compound. The catalyst compound comprises the product resulting from contacting an onium salt, amine, or amine salt with an acid or a salt of an acid having a weak nucleophilic anion.
U.S. Pat. No. 5,134,239 (Bertram et al.) teaches the use of latent catalyst compounds for catalyzing the reaction between epoxide and aromatic hydroxyl groups. These catalysts are prepared by contacting a nitrogen-containing heterocyclic compound with an acid having a weak nucleophilic anion.